WATER SUPPLY ENGINEERING

1. UNIT-II

2. CHAPTER 2.1
TREATMENT OF WATER

3. SEDIMENTATION
• It is the process of causing heavier solid
particles in suspension both organic and
inorganic, to settle by retaining water in a
basin

4. Sedimentation

5. THEORY OF SEDIMENTATION
• The particles heavier than water tends to
settle down due to force of gravity.
• Impurities in water are held in suspension
due to the turbulence of the moving water.
• When the velocity of flow is reduced, the
suspended particles tend to settle down at the
bottom of the tank.
• This phenomenan is known as hydraulic
subsidence.

6. FACTORS AFFECTING SEDIMENTATION
• Size, shape and weight of the particle
• Viscosity and temperature of water
• Surface overflow
• Surface area
• Velocity of flow
• Inlet and outlet arrangements
• Detention period

7. • Effective depth of settling tank
• Concentration of suspended matter
• Wind blow on the surface area of the basin
• Biological, electrical and other forces

8. TYPES OD SEDIMENTAION
• PLAIN SEDIMENTATION
• SEDIMENTATION WITH COAGULATION

9. PLAIN SEDIMENTATION
• The raw water is retained for sometime in a
basin for the suspended particles to settle
down by the action of gravity.

10. SEDIMENTATION WITH COAGULATION
• In this some chemical compounds called
coagulants are added to water to assist
sedimentation.

11. Coagulation

12. Classification of sedimentation tank
• Nature of working
 Fill and draw type
 Continuous flow type
• Direction of flow
 Horizontal flow basin
 Vertical or upward flow basin
 Radial flow basin
 Spiral or circumferential flow basin

13. • Shape
 Rectangular(horizontal flow) tanks.
 Circular (vertical, radial, circumferential flow)
tanks.
 Hopper bottom (radial flow) tanks.

14. FILL AND DRAW TYPE
• The raw water is allowed to rest on the basin
for sometime.
• During that time the suspended particles
settle down at the bottom.
• The clear water is drawn off and the deposits
are cleaned.
• Then the basins is refilled and the action
continues.

16. CONTINUOUS FLOW TYPE
• The raw water is allowed to flow through the
tank continuously with a small uniform
velocity.
• Within the detention time the suspended
particles settle down at the bottom before
they reach the exit.
• The inlets and outlets are so designed that
they cause least disturbance to the flowing
water in the tank.

18. HORIZONTAL FLOW BASIN
• It is a rectangular plan having length is twice
or thrice the breadth.
• The floor is given a slope to facilitate sludge
removal.

19. VERTICAL OR UPWARD FLOW BASIN
• It is deep and circular or rectangular with
hopper bottom.
• The raw water enters the basin vertically from
bottom through the centrally located vertical
inlet pipe.
• The suspending particle settle down at the
hopper bottom and is collected through the
sludge pipe.

21. RADIAL FLOW BASIN

22. • The water enters through the central inlet
pipe.
• The inlet pipe is enclosed with the deflector
box which deflects the flow downwards.
• Then the flow goes out radially towards the
circumference of the tank.
• During the radial flow all the settleable
particles settle down.

23. SPIRAL OR CIRCUMFERENCE FLOW
BASIN

24. • The water enters the tank through two or
three vertical slits of the inlet channel.
• A rotating arm is provided in the tank.
• It makes all the water in the tank to move
circumferentially.
• As the flow is very slow all the settleable
particles settle at the bottom of the tank.
• Clear water is drawn through weir type outlet.

25. DEFINITION IN COAGULATION OF
WATER
• The process of addition and mixing of
coagulants is coagulation.
• The process of addition of coagulants in
correct amount is called dosing.
• The process of floc formation is termed as
flocculation.
• The coagulation is adopted when the turbidity
of raw water exceeds 30 to 50 ppm.

26. Objectives of coagulants
• To unite several fine colloidal particles
together.
• To react with impurities in water and make
them to settle.
• To prepare raw water fit for filtration.
• To expedite quick sedimentation.
• To remove certain extent turbidity, organic
and inorganic matter.

27. COMMON COAGULANTS
• Sodium aluminate
• Ferric chloride
• Ferric sulphates
• Betonite clay
• Fuller’s earth
• Magnesium carbonate
• Polyelectolytes

28. COAGULANT FEEDERS
• The coagulants may be fed in powder form
(dry feeding) or in solution form (wet feeding)
Dry feeders
Wet feeders

29. DRY FEEDERS

30. WET FEEDERS

31. COAGULANT MIXERS
• The success of floc formation mainly depends
upon the through mixing of coagulant with raw
water
• The violent mixing is carried out by the following
devices
Centrifugal pump
Compressed air
Mixing channel
Mixing basin

32. Mixing basins with baffle walls
• Horizontal or round the end type
• Vertical or over and under the baffle type

34. Mixing basins with mechanical devices
• Flash mixers
• Flocculators

36. DOSAGE OF COAGULANTS
• Kind of coagulants
• Amount of coagulants
• Time of mixing
• Violence of agitation
• Time of settlement
• Amount and character of colour
• Turbidity of water
• Ph of water
• Temperature of water

37. FILTRATION
• Filtration is the process of passing the water
through filter beds.
• Filtration is the most important stage in the
purification of water.
• Filtration removes colour, odour, turbidity and
pathogenetic bacteria from water
• It also changes the chemical characteristics of
water.

38. THEORY OF FILTRATION
Mechanical straining
Sedimentation and absorption
Biological metabolism of bacterial action
Electrolytic changes

40. FILTER SAND
• Sand having effective size of 0.25 to 0.35 mm
are used for slow sand filters
• Sand having effective size of 0.35 to 0.60 mm
are used for rapid sand filters
• For slow sand filters the depth of sand bed is
0.60 to 1m.
• For slow sand filters the depth of sand bed is
0.60 to 0.9m.

41. TYPES OF FILTERS
• Slow sand filters
• Rapid sand filters
• Pressure filters

46. DISINFECTION OF WATER
• Disinfection of water is the process of removal
of pathogenic bacteria from water by
chemicals.
• The chemicals used for killing disease
producing bacteria is known as disinfectants.
• Sterilisation is the process of killing all bacteria
by boiling.

47. METHODS OF DISINFECTION
• Boiling
• Excess lime treatment
• Iodine and bromine treatment
• Ozone treatment
• Potassium permanganate treatment
• Silver treatment
• Ultra violet ray treatment

48. CHLORINATION
• Chlorination is the treatment of water with
chlorine for disinfection of water.
• Chlorination not only disinfectants, but also
removes colour, odour, unpleasant taste and
prevent the growth of weeds in water.

49. FORMS OF CHLORINATION
• As bleaching powder
• As chloromines
• As chlorine-di-oxide
• As free chlorine gas
• As liquid chlorine

50. • Dosage of chlorine
• Residual chlorine
• Contact period

51. WATER SOFTENING
• Water softening is the process of reduction of
hardness of water
Purpose of water softening
To reduce soap consumption
To reduce corrosion
To improve the taste of food
To reduce scaling in boilers

52. HARDNESS OF WATER
• It is caused by the presence of certain salts of
calcium and magnesium dissolved in water.
• It s the characteristic which prevents the
lathering of soap.
• TYPES OF HARDNESS
Temporary hardness
Permanent hardness

53. REMOVAL OF HARDNESS
• Removal of temporary hardness
• Removal of permanent hardness
Lime – soda process
Zeolite process
Demineralisation

54. MISCELLANEOUS METHODS FOR
TREATMENT
• Removal of colour, odour, taste
Aeration
Activated carbon treatment
Copper sulphate treatment
Oxidation of organic matter
• Removal of iron and manganese
• Fluoridation and defluoridation

55. REVERSE OSMOSIS PROCESS

56. CHAPTER 2.2
DISTRIBUTION SYSTEM

57. GENERAL REQUIREMENTS
• It should be capable of supplying water in
adequate quantities.
• It should meet the demand of water supply for
fire fighting purposes.
• It should be economical in its design, layout and
construction.
• It should be easy and simple to operate and
repair.
• It should be safe against any future pollution of
water

58. • It should be water tight.
• It should be safe as not to cause the failure of
the pipe line.
• It should provide free circulation of water.
• The sanitation of the water distribution area
should be good so that the possibilities of
pollution are remote during repairs or
replacement of pipes.

59. DIFFERENT SYSTEMS OF SUPPLYING
WATER
Systems of conveyance and distribution
Systems of water supply
Systems of distribution layout

60. SYSTEMS OF CONVEYANCE AND
DISTRIBUTION
• Gravity system
• Pumping system
• Combined pumping and gravity system

61. SYSTEM OF WATER SUPPLY
• Continuous system
• Intermittent system.

62. SYSTEM OF DISTRIBUTION LAYOUT
• Dead end or tree system
• Grid iron system
• Circular or ring system
• Radial system

63. SERVICE RESERVOIRS
• Service reservoir are also known as
distribution reservoir.
• They are the tanks constructed to store
treated water which may be used when
required.

64. FUNCTIONS OF SERVICE RESERVOIR
• To store water for emergencies like breakdown
of pumps, fires, power supply failures etc…
• To facilitate constant rate of pumping and thus
reduce pumping hours.
• Under gravity system of supply, to minimise
the diameter of mains.
• To make the design and construction of
treatment units and distribution system
economical.

65. TYPES OF SERVICE RESERVOIR
• SURFACE RESERVOIR
• ELEVATED RESERVOIR

66. CAPACITY OF SERVICE RESERVOIR
Balancing storage
Breakdown storage
Fire storage

67. FACTORS AFFECTING CAPACITY OF
RESERVOIRS
• The variation between maximum and
minimum demands.
• The reserve required for emergencies like fire
or breakdown of pumps.
• The standby pumping capacity.
• Interconnections in the distribution mains.